Mild and Effective Method for the Nickel-Catalyzed Arylation of Glycosyl Thiols in Aqueous Surfactant Solution

Aryl thioglycosides have broad applicability as both glycosyl donors and glycomimetic compounds. Their synthesis via the cross-coupling of glycosyl thiols with aryl halides has become a popular method for their construction because it allows better selectivity for anomeric configuration as well as a wider functional group tolerance compared to traditional methods. Herein, we report a nickel-catalyzed method for the synthesis of aryl thioglycosides which utilizes an aqueous micellar environment as the reaction medium. This alternative method allows for mild conditions while circumventing expensive palladium, leading to the successful synthesis of over 30 aryl thioglycosides, including challenging 1,2-cis thioglycoside products.

Pd-Catalyzed Synthesis of 1-(Hetero)aryl Thioglycosides: Strategy for the Trapping of an Acyl Group of Glycosylthioesters by Coupling of Bis-Electrophilic-Nucleophilic Partners

Herein, we describe a stereoretentive palladium-catalyzed cross-coupling between the in situ-generated glycosyl thiolate anion and diverse (hetero)aryl iodides at room temperature for creating the library of (hetero)aryl thioglycosides. The key to success is the judicious pairing of bis-electrophilic-nucleophilic partners with a variety of thioesters in an atom-economical way in which both the glycosyl thiolate anion and the acylium cation are incorporated into the final analogue. The advantage of this method is the acyl transfer on various nucleophilic partners, including a hydroxyl, a primary or secondary amine, an amino acid, and the biologically active hSGLT1 inhibitor.

Electrochemical nickel-catalyzed cross-coupling of glycosyl thiols with preactivated phenols and ketones

An efficient electrochemical nickel-catalyzed cross-coupling reaction has been reported here for the synthesis of S-glycosides from preactivated phenols and ketones under mild conditions. Various glycosyl thiols, including unprotected sugar, and a diverse range of aryl/alkenyl triflates, including some complex biorelevant phenols and ketones, were well tolerated in this method.

Electrochemical Nickel-Catalyzed Selective Inter- and Intramolecular Arylations of Cysteine-Containing Peptides

Here we report a simple electrochemical route towards the synthesis of S-arylated peptides by a site selective coupling of peptides with aryl halides under base free conditions. This approach demonstrates the power of electrochemistry to access both highly complex peptide conjugates and cyclic peptides.

Visible-light-mediated synthesis of non-anomeric S-aryl glycosides via a photoactive electron-donor-acceptor complex

A visible-light-mediated glycosylation reaction between glycosyl redox-active esters and disulfides has been reported, through which a series of S-aryl glycosides were obtained in good yields with satisfactory stereoselectivity. The preliminary mechanistic studies revealed that this transformation proceeded via an EDA complex. Moreover, the potential application value was demonstrated in the late-stage functionalisation of drug molecules and a gram-scale experiment.

A Robust Copper-Catalyzed Cross-Coupling of Glycosyl Thiosulfonate and Boronic Acids Enables the Construction of Thioglycosides

An efficient and stereoretentive copper-catalyzed cross-coupling of glycosyl thiosulfonate and boronic acid for the construction of thioglycosides is described. The good functional group compatibility of this method allows the preparation of many bioactive aryl/alkenyl thioglycosides, including the hSGLT1 inhibitor.

Atom-Economic Synthesis of Unsymmetrical gem-Diarylmethylthio/Seleno Glycosides via Base Mediated C(O)-S/Se Bond Cleavage and Acyl Transfer Approach of Glycosylthio/Selenoacetates

Herein, we invented the Cs₂CO₃-mediated atom economic method that streamlines the scission of the C(O)-S/Se bond involving the in situ generation of an anomeric thiolate/selenolate anion, which reacted with p-QMs to yield novel unsymmetrical gem-diarylmethylthio/seleno glycosides while retaining the anomeric stereochemistry. Notably, the key features of this protocol involve unprecedented long-range acyl transfer (from S/Se to O), thus affording acylation of the final product which is not yet reported by classical methods. This straightforward protocol offers a mild, short reaction time, synthetically simple approach, and compatibility with 8 types of sugar along with phenylthio/benzylseleno esters.

Copper(I)-Catalyzed Sandmeyer-Type S-Arylation of 1-Thiosugars with Aryldiazonium Salts under Mild Conditions

Preparation of S-aryl thioglycosides from 1-thiosugars via S-arylation was demonstrated under mild reaction conditions. A wide range of protected and unprotected 1-thiosugars derived from glucose, glucosamine, galactose, mannose, ribose, maltose, and lactose underwent cross-coupling reactions with functionalized aryldiazonium salts in the presence of copper(I) chloride and DBU. The desired products were obtained in 55-88% yields within 5 min. Various functional groups, including halogens, were tolerated under standard reaction conditions. Synthesis of the biologically relevant antidiabetic dapagliflozin S-analogue and arbutin S-analogues (tyrosinase inhibitors) was demonstrated.

Visible-Light-Mediated Stadler-Ziegler Arylation of Thiosugars with Anilines

Here, we report a one-pot Stadler-Ziegler reaction toward the synthesis of 1-thioglycosides in good yield from commercially available anilines and (un)protected 1-glycosyl thiols. This simple and mild approach employs the photoredox catalyst [Ru(bpy)₃](PF₆)₂ under visible light.

Nickel-Catalyzed Paired Electrochemical Cross-Coupling of Aryl Halides with Nucleophiles

Electrochemistry has recently gained increased attention as a versatile strategy for achieving challenging transformations at the forefront of synthetic organic chemistry. However, most electrochemical transformations only employ one electrode (anodic oxidation or cathodic reduction) to afford the desired products, while the chemistry that occurs at the counter electrode yields stoichiometric waste. In contrast, paired electrochemical reactions can synchronously utilize the anodic and cathodic reactions to deliver the desired product, thus improving the atom economy and energy efficiency of the electrolytic process. This review gives an overview of recent advances in nickel-catalyzed paired electrochemical cross-coupling reactions of aryl/alkenyl halides with different nucleophiles.

1 Introduction

2 Nickel-Catalyzed Cross-Coupling Reactions

2.1 C–C Bond Formation

2.2 C–N Bond Formation

2.3 C–S/O Bond Formation

2.4 C–P Bond Formation

3 Conclusion

Recent advances in organic electrosynthesis employing transition metal complexes as electrocatalysts

Organic electrosynthesis has been widely used as an environmentally conscious alternative to conventional methods for redox reactions because it utilizes electric current as a traceless redox agent instead of chemical redox agents. Indirect electrolysis employing a redox catalyst has received tremendous attention, since it provides various advantages compared to direct electrolysis. With indirect electrolysis, overpotential of electron transfer can be avoided, which is inherently milder, thus wide functional group tolerance can be achieved. Additionally, chemoselectivity, regioselectivity, and stereoselectivity can be tuned by the redox catalysts used in indirect electrolysis. Furthermore, electrode passivation can be avoided by preventing the formation of polymer films on the electrode surface. Common redox catalysts include N-oxyl radicals, hypervalent iodine species, halides, amines, benzoquinones (such as DDQ and tetrachlorobenzoquinone), and transition metals. In recent years, great progress has been made in the field of indirect organic electrosynthesis using transition metals as redox catalysts for reaction classes including C-H functionalization, radical cyclization, and cross-coupling of aryl halides-each owing to the diverse reactivity and accessible oxidation states of transition metals. Although various reviews of organic electrosynthesis are available, there is a lack of articles that focus on recent research progress in the area of indirect electrolysis using transition metals, which is the impetus for this review.

Synthesis of axially chiral biaryl thioglycosides through thiosugar-directed Pd-catalyzed asymmetric C-H activation

Herein we report for the first time that the thiosugar moiety can be used both as a directing group enabling the regioselective activation of a C-H bond of biaryl scaffolds and as a chiral source inducing axial chirality. Our approach enables the easy generation of complex thioglycoside atropoisomers, thus paving the way to new products of potential biological interest.

Modular Synthesis of Aryl Thio/Selenoglycosides via the Catellani Strategy

We described a novel palladium-catalyzed domino procedure for the preparation of (hetero)aryl thio/selenoglycosides. Readily available (hetero)aryl iodides and easily accessible 1-thiosugars/1-selenosugars are utilized as the substrates. Meanwhile, 10 types of sugars are quite compatible with this reaction with good regio- and stereoselectivity, high efficiency, and broad applicability (up to 89%, 53 examples). This method enables the straightforward formation of the C(sp²)-S/Se bond of (hetero)aryl thio/selenoglycosides.

Transition-metal-free synthesis of aryl 1-thioglycosides with arynes at room temperature

A mild, convenient and transition-metal-free protocol for the synthesis of aryl 1-thioglycosides is presented via arynes generated in situ combined with glycosyl thiols in the presence of TBAF(tBuOH)₄. The methodology provides a general and efficient way to prepare a series of functionalized thioglycosides in good to excellent yields with a perfect control of the anomeric configuration at room temperature. In addition, the reaction conditions tolerate a variety of the pentoses and hexoses, and the reaction also performs smoothly on protected monosaccharides and disaccharides.

Electrocatalysis as an enabling technology for organic synthesis

Electrochemistry has recently gained increased attention as a versatile strategy for achieving challenging transformations at the forefront of synthetic organic chemistry. Electrochemistry's unique ability to generate highly reactive radical and radical ion intermediates in a controlled fashion under mild conditions has inspired the development of a number of new electrochemical methodologies for the preparation of valuable chemical motifs. Particularly, recent developments in electrosynthesis have featured an increased use of redox-active electrocatalysts to further enhance control over the selective formation and downstream reactivity of these reactive intermediates. Furthermore, electrocatalytic mediators enable synthetic transformations to proceed in a manner that is mechanistically distinct from purely chemical methods, allowing for the subversion of kinetic and thermodynamic obstacles encountered in conventional organic synthesis. This review highlights key innovations within the past decade in the area of synthetic electrocatalysis, with emphasis on the mechanisms and catalyst design principles underpinning these advancements. A host of oxidative and reductive electrocatalytic methodologies are discussed and are grouped according to the classification of the synthetic transformation and the nature of the electrocatalyst.

Nickel-Catalyzed N-Arylation of NH-Sulfoximines with Aryl Halides via Paired Electrolysis

A novel strategy for the N-arylation of NH-sulfoximines has been developed by merging nickel catalysis and electrochemistry (in an undivided cell), thereby providing a practical method for the construction of sulfoximine derivatives. Paired electrolysis is employed in this protocol, so a sacrificial anode is not required. Owing to the mild reaction conditions, excellent functional group tolerance and yield are achieved. A preliminary mechanistic study indicates that the anodic oxidation of a Ni^II species is crucial to promote the reductive elimination of a C-N bond from the resulting Ni^III species at room temperature.

Recent advances in the direct O-arylation of carbohydrates

Methods for the O-arylation of hydroxyl and hemiacetal groups in carbohydrates via C(sp2)-O bond formation are discussed. Such methods provide an alternative disconnection to the traditional approach of nucleophilic substitution between a sugar-derived electrophile and a phenol or phenoxide nucleophile. They have led to new opportunities for stereoselectivity, site-selectivity and chemoselectivity in the preparation of O-aryl glycosides and carbohydrate-derived aryl ethers, compounds that are useful for a broad range of applications in medicinal chemistry, glycobiology and organic synthesis.

Recent Advances in Metal-Catalyzed, Electrochemical Coupling Reactions of sp2 Halides/Boronic Acids and sp3 Centers

Traditionally, metal-catalyzed cross-coupling reactions rely on stable but expensive metals, such as palladium. However, the recent development of synthetic organic electrochemistry allows for in situ redox manipulations, expanding the use of cheaper, abundant and sustainable metals, such as nickel and copper as efficient cross-coupling catalysts. This short review covers the recent advances in metal-catalyzed electrochemical coupling reactions, with a focus on reactions of sp2 electrophiles and nucleophiles with sp3 coupling partners to form both C–C and C–heteroatom bonds.

1 Introduction

2 Nickel-Catalyzed C–C sp2–sp3 Coupling Reactions

3 Coupling of Aryl Groups with Heteroatomic Nuclei

4 Conclusion